Not applicable.
This invention relates to the authentication of visual images such as are produced by a video camera or the like, and more particularly to a method of authentication employing algorithms to encode information by which the image can be authenticated.
There are a variety of situations in which it is important to know that a visual image such as an image transmitted from one location to another, or a stored image which is to be used at a later time is provided or maintained in the exact form in which it was produced. In the medical field, for example, it is now commonplace to transmit a picture (a visual image) of a patient from one site (a local hospital, for example) to another (the location of a specialist). The image may be an x-ray, CAT scan image, or other image of the patient. Because the image may be used in making a diagnosis, describing a medication or course of treatment, or viewed by a specialist while surgery is being performed, any inaccuracies in the received image can potentially have serious consequences. And, it is known that transmission errors due to noise on the transmission line, temporary disruptions, etc. do occur.
As a further example, many police interrogation rooms are equipped with video equipment so the police examination of a suspect can be recorded. The resulting record can then be used for evidentiary purposes, as well as to defend the police against charges by a suspect that he was mistreated or that a confession was forced from him.
In security systems, to use another example, a video system may capture the image of an intruder during an unauthorized entry. The image therefore can become part of the evidence which is used to prosecute a suspect. To use the image as evidence against the suspect at trial, it is necessary to maintain the image in its original form and do so in a way that the custodian of the evidence can clearly demonstrate to a court that the image has not been tampered with. It is well known that technology exists by which images can be modified. Such technology can be used to alter the image in such a way that its evidentiary value is destroyed. It is thus important to provide a foolproof method by which tampering can be prevented, or if tampering occurs, it is readily discernible.
In the above referenced patent application, a method was described in which a 2-dimensional pixel matrix representing an image to be authenticated was created from an image frame. From this matrix, a second 2-dimensional matrix was created in accordance with certain rules. A first linear vector was then formed from the second 2-dimensional matrix, and a second linear vector was created by reforming blocks of information from the first linear vector. A checksum value was then determined. This value was then attached to a header of the image frame and retained with the frame for subsequent authentication of the contents of the image and to serve as an indication if the image contents had been tampered with. This application addresses improvements in this authentication methodology.
In particular, formation of the second 2-dimensional array in the co-pending application was done by eliminating certain rows and columns from the first 2-dimensional array in accordance with a set of rules. From an evidentiary standpoint, a defendant whose image is captured in an authenticated video image might try to argue that because the pixels in the eliminated rows and columns were xe2x80x9cnot touchedxe2x80x9d by the authentication process, the image does not have evidentiary value. While this is untrue, it may be easy to see why attempting to explain this methodology to a judge and jury could confuse them. Accordingly, the method has been modified so that as part of the authentication process, every pixel comprising the image being authenticated is now xe2x80x9ctouched,xe2x80x9d and the results of that xe2x80x9ctouchingxe2x80x9d is included with the other authentication information. In addition, other event relation is now included with the first 2-dimensional array prior to performing the other steps in the authentication process.
Among the several objects of the present invention may be noted the provision of a method of authenticating visual images so to prevent tampering with the image, or if the image is transmitted from one location to another, to make it easy to determine if the image which was received exactly corresponds with that which was transmitted;
the provision of such an authentication method in which data representing the content of the whole or a portion of the image is encrypted at the time the image is produced with this encrypted portion of the image being maintained with the entire image for subsequent authentication of the image;
the provision of such a method in which the encryption of the portion of the image is accomplished using an algorithm that has as a factor elements of the time at which the image is produced, these elements including the month, day, hour, and minute at which the image is produced;
the provision of such a method in which the image content encryption code changes minute by minute, so the results from the encryption of an image at one minute produces an authentication code which is different from the authentication code which would result if the encryption were made a minute earlier or a minute later;
the provision of such a method by which, once the image is authenticated, if the image subsequently tampered with, or otherwise altered, such tampering or alteration is not only immediately discernible, but the portion of the image which has been tampered with or altered can be readily identified;
the provision of such a method by which the visual image is converted to a data format arranged in a first array and subsequently processed through successive arrays or linear vectors as part of the encryption process;
the provision of such a method to employ a cyclical redundancy check by which every pixel comprising the image is processed, the results of this processing being retained with the other authentication information;
the provision of such a method in which a total image checksum value is ultimately derived for the processed image, the checksum value then being placed in a header attached to the original image, the image and header then being stored or transmitted together so the checksum information can be used to provide image authentication;
the provision of such a method in which bits identifying the camera with which the image is taken, time and place of the event, and other related information are also processed together with the image pixels whereby the total image checksum includes camera identification and other event related information;
the provision of such a method to further include in the header information as to where the image was taken and the time at which the image was formed;
the provision of such a method in which encryption codes used in the algorithm used can be varied from one location to another, and in which the codes are periodically changed;
the provision of such a method which is useful, for example, in transmitting pictorial medical information from one location to another to verify that an image which is received corresponds with that transmitted, or in a security system for monitoring a facility and detecting a breach in security at the facility, especially where evidence of the breach is captured by a camera and it is important to subsequently authenticate the image produced for use by law enforcement officials, or in court; and,
the provision of such a method in which the algorithm used for producing the authentication is readily incorporated in image processing equipment located at the site where images are produced so authentication for the image can be created when the image is produced.
In accordance with the invention, generally stated, a method is taught for authenticating a video image created by a camera or other video device. The visual image is transformed into a data format with a 2-dimensional array being created in which each pixel forming the image is represented by a data word of predetermined length. This array may be converted into a second 2-dimensional array of a size different than that of the first array to reduce the required data transmission rate. This is not an essential part of the algorithm but may simply be a practical necessity. It will be understood that the algorithm works for all pixel formats (512xc3x97480, 384xc3x97288, etc.). This conversion is performed using a set of rules by which certain rows and columns in the formatted array are eliminated. A first linear vector is now formed and includes the data words transferred from the first to the second 2-dimensional array. A second linear vector is formed by rearranging the data words in the first linear vector, the new locations of the data words in the second linear vector being randomly selected. Camera identification, time, place and other relevant information are also included in the vector. A total image checksum is determined using the data words as arranged in the second linear vector. A cyclical redundancy check is also performed, this check involving all the pixels forming the image. A header is created using the resulting checksum and cyclical redundancy check results, and other relevant information. This header is attached to the formatted array. Other objects and features will be in part apparent and in part pointed out hereinafter.